Receiver for providing an activation signal to a device

ABSTRACT

A receiver ( 30 ) for providing an activation signal ( 54 ) to transition a device from a dormant state to an operative state. The receiver includes a sensor ( 32 ), a super regenerative oscillator, SRO, circuit ( 34 ), and a processing device ( 36, 38 ). The sensor is one of an optical sensor, an acoustic sensor, and a magnetic field sensor, and generates detector signals ( 40 ) based on wireless signals ( 28 ) received from an external source ( 18 ). The SRO circuit is electrically coupled to the sensor to receive the detector signals, and electrically oscillates with a constant SRO frequency and with a SRO amplitude (As) that changes when a carrier frequency of the detector signal substantially matches the SRO frequency. The processing device monitors the SRO amplitude in time, and generates the activation signal when a temporal characteristic (Sc) of the monitored SRO amplitude matches a predetermined reference pattern ( 52 ).

TECHNICAL FIELD

The invention relates to a receiver for providing an activation signalto a device to transition the device into an operative state, and to aunit including such a receiver. Furthermore, the invention relates to amethod for transitioning a unit into an operative state, and to acomputer readable medium for carrying out the proposed method.

BACKGROUND ART

In power-constrained electronic devices such as wireless communicationand/or sensing devices, energy efficiency is a critical designconsideration. Such power-constrained devices may be battery operated,solar powered, restricted in waste heat discharging capability, orotherwise limited in their allowed power consumption. Power-constrainedsensing or communication devices typically include a wirelesstransceiver that has significant power requirements. Suchpower-constrained system may nevertheless be required to functionautonomously for a prolonged time (e.g. several months to years), toreduce deployment, maintenance, and retrieval operations to a minimum.As an example, deep-sea instruments may be deployable on the seafloorfor sensing/monitoring operations. The hostile underwater conditions indeep-sea environments, with typical ocean floor depths in the order ofseveral kilometers, severely hinder maintenance and retrievaloperations.

Such and other power-constrained devices may benefit from an ability totoggle between an active mode (“operative state”) in which the device isfully functional, and a standby mode (“dormant state”) in which mostsub-systems are switched off to reduce energy consumption when executionof sensing/communication functions is not desired. When the timingrequirements for toggling between the states are known in advance, itmay suffice to implement an internal mode-toggling scheme in thedevice's own controller. However, if the timing schedule or otherconditions for toggling between states cannot be defined in advance, itmay be beneficial to implement a wake-up signaling scheme that allows anexternal source to send a signal to the device and cause it to changestate.

Correspondingly, it would be desirable to provide a wake-up receiver fortransitioning a device from a dormant state to an operative state, whichachieves a good balance between energy consumption, sensitivity, andselectivity.

SUMMARY OF INVENTION

Therefore, according to a first aspect of the invention, there isprovided a receiver that is configured to provide an activation signalto a device in order to transition the device from a dormant state to anoperative state. The receiver comprises a sensor, a super regenerativeoscillator (SRO) circuit, and a processing device. The sensor is one ofan optical sensor, an acoustic sensor, and a magnetic field sensor, andis configured to receive a wireless signal from an external source andto generate a detector signal in response to the received wirelesssignal. The SRO circuit is electrically coupled to the sensor to receivethe detector signal, and configured to electrically oscillate with aconstant SRO frequency and with a SRO amplitude that changes when acarrier frequency of the detector signal substantially matches the SROfrequency. The processing device is configured to monitor the SROamplitude in time, and to generate the activation signal when a temporalcharacteristic of the monitored SRO amplitude matches a predeterminedreference pattern.

The proposed receiver includes a low power circuit for sending anactivation signal to the device. Said circuit may be designed as awake-up circuit. The device remains in a dormant (“standby”) state whenthe device is not required to operate, to minimize power consumption andconserve energy. The SRO-based receiver may be efficiently used inpower-constrained systems.

The sensor may be an optical sensor (e.g. a photodiode or lightdependent resistor), an acoustic sensor (e.g. a hydrophone), or amagnetic field sensor (e.g. a magnetometer). Correspondingly, thewireless signal may be a wireless optical signal, a wireless acousticsignal, or a wireless magnetic field signal. Such sensors and wirelesssignal carriers are particularly suitable in environments with ambientfluids that exhibit high absorption of radio-frequency electromagneticwaves, for instance in underwater settings. The term “wireless” is usedherein to refer to the transfer of information between objects that areat different locations, and which are not interconnected by wires butexchange signals via waves emitted and/or received via the fluid mediumor vacuum that surrounds these objects.

When the sensor receives a wireless signal from a source in thevicinity, it generates a detector signal, e.g. an electrical potentialdifference or electrical current. This detector signal varies in time inresponse to changes in the received signal amplitude, and is injectedinto the SRO circuit. The SRO circuit may additionally be driven by aperiodic electric current or voltage that brings the SRO into and out ofelectrical oscillation. The SRO circuit can be made to oscillate at theSRO resonance frequency, and will predominantly respond to detectorsignals with carrier frequencies that are substantially equal to the SROfrequency. Here, i.e. in the specification and the claims, the term“substantially” refers to a situation where the carrier frequency isclose to the SRO frequency, i.e. preferably within a range of ±10%, morepreferably within arrange of ±5%, and most preferably within a range of±1% of the SRO frequency. The term “carrier frequency” is used herein torefer to a fundamental harmonic amplitude variation in the disturbanceof the carrying medium itself, e.g. periodic oscillation of the fluidparticles in the case of sound, or low-frequency periodic oscillation ofthe magnetic field in non-radiative/inductive coupling, or an additionalharmonic amplitude modulation with a lower frequency that is superposedonto the fundamental oscillation of the carrying medium, e.g. harmonicAM in the case of light. In order to successfully address the receiver,the external source should be able to generate a wireless signal with acarrier frequency falling within the SRO's peak resonance response, andto further modulate this carrier frequency signal with the predeterminedreference pattern, e.g. based on amplitude-shift keying. When a wirelesssignal with a right carrier frequency and data signature is picked-up bythe sensor, filtered by the SRO, and tracked in time and recognized bythe processing device, the latter will generate a wake-up signal.

The SRO circuit functions as a frequency-selective filter, e.g. bandpassfilter, which only generates a deviating amplitude response, i.e.different from default amplitude variation upon receiving detectorsignals with a carrier frequency that substantially matches with the SROcenter frequency. Detection signals with carrier frequencies that areoutside, i.e. higher or lower than the SRO's resonance peak cause nonoticeable response. The SRO circuit is highly sensitive to signals witha matching carrier frequency, and generates a substantial SRO amplitudechange even for detector signals with small amplitudes. The receivertherefore provides a large gain for received signals with a carrierfrequency that matches the SRO frequency.

In an embodiment, the SRO circuit is configured to electricallyoscillate with a varying SRO amplitude during successive time intervals.The SRO amplitude may be quenched at a start of each time interval andmay subsequently rise during said time interval. A rising rate for theSRO amplitude within said time interval may be magnified when thecarrier frequency of the detector signal substantially matches the SROfrequency. The processing device may then be configured to determinecharacteristic times for the rise of the SRO amplitude during each ofthe time intervals to derive the temporal characteristic.

A characteristic time required for the SRO amplitude to increase in aparticular time interval from (virtually) zero to a reference amplitudewill vary as function of detector signal amplitude. If the sensor is notreceiving a wireless signal and not generating a detector signal (apartfrom noise), it takes the SRO a first characteristic time to bring theSRO oscillation amplitude to the reference level. If the sensor picks upa wireless signal with a carrier wave at or near the SRO centerfrequency, it takes the SRO a second characteristic time shorter thanthe first time to bring the oscillation amplitude up to the referencelevel. The SRO oscillation thus rises more rapidly when receiving adetector signal at/near the SRO frequency, with the rate of increasebeing dependent on the amplitude of the wireless signal. By measuringthe characteristic time for each time interval, the amplitude modulationof received wireless signals with matching frequency may be transformedinto a time-domain signal. The SRO oscillation may be impressed by anexternal periodic signal source that alternatingly drives and quenchesthe oscillations in the SRO circuit.

The SRO circuit may be configured to let the rate of increase of theoscillation amplitude vary in time as a logarithmic function of anamplitude of the detector signal. Letting the characteristic time Tivary as a logarithmic function of the detector signal amplitude Ar—i.e.Ti∝log(k·Ar)—allows the SRO circuit to provide automatic gain control.Relatively small detector signal amplitudes (compared to no detectorsignal) already causes noticeable Ti-shortening, whereas furtherTi-shortening for larger detector signals follows a logarithmic trend.In this manner, large detector signal amplitudes, e.g. from a sourcethat is nearby and/or emits signals with a high spectral power at theSRO frequency, do not immediately drive the SRO into maximumoscillation.

In embodiments, the processing device comprises a comparator that isconfigured to receive an output signal with said varying SRO amplitudefrom the SRO circuit, and is configured to output a comparator signalwith a distinct value if the varying SRO amplitude exceeds a referenceamplitude.

In further embodiments, the receiver comprises a microcontroller that iselectrically coupled to the comparator and configured to receive andstore said comparator signal with a sequence of consecutive distinctvalues in time, to compare the sequence of consecutive distinct valuesto said predetermined reference pattern, and to generate the sequence ofconsecutive distinct values matches said predetermined referencepattern.

The varying characteristic startup times Ti for the SRO may be analyzedby the microcontroller, which scans for a potential presence of apredetermined pattern in the sequence of comparator signals bycomparison with a reference pattern. The microcontroller may forinstance be formed as a programmable system-on-chip (PSoC), and includea shift register for storing an updated sequence of consecutivecomparator signals in time, including the most recent comparator signaland a predetermined integer number of preceding comparator signals.After each measurement and update, the microcontroller may compare theupdated sequence with the reference sequence to determine if they match,and to generate the activation signal is this is the case.

In further embodiments, the microcontroller is electrically coupled tothe SRO circuit, and configured to generate and impose onto the SROcircuit a driving signal that is superimposed upon the detector signal.The SRO may thus be controlled by a periodic driving signal that isgenerated by the same microcontroller that also measures thecharacteristic time delays Ti. This functional integration helps toreduce power consumption. The driving signal may form an alternatinglyrising and falling signal that is configured to periodically induce andquench oscillations in the SRO circuit.

The driving signal may for instance be a periodic quench-ramp signalwith a sawtooth profile, which is alternatingly formed by slowly risingedges that incite SRO oscillations, and steeply falling edges thatquench the SRO oscillations. Falling edges of the ramping signal may beregularly paced to mark each start of a time slot Δti, and acharacteristic time Ti between a falling edge of the driving signal andthe next moment SRO oscillations start depends on the amplitude of the(frequency-matching) detector signal.

In alternative embodiments, the SRO circuit may be “self-quenching”,which refers to an architecture in which the SRO circuit itself causesthe oscillation to quench as soon as the oscillation amplitude hasreached a threshold value.

According to an embodiment, the sensor is an optical sensor including aplurality of avalanche photodiode (APD) elements. The APD elements maybe arranged in an array and form part of a silicon photomultiplier(SiPM) sensor. The considerable photon detection efficiency, highdetection gain, and fast response time of a SiPM sensor render thissensor type particularly suitable for optical detection and wirelessoptical communication in environments with low levels of ambient light,for instance for light detection and/or communication between entitiesthat are deployed in a subsea environment at distances of several, up tohundreds of meters.

In alternative embodiments, the optical sensor may include a pluralityof light dependent resistor (LDR) elements.

According to embodiments, the SRO circuit comprises a frequencyselective element and a gain element, which frequency selective elementis tuned to said carrier frequency. In further embodiments, a gain ofthe gain element is controlled by said driving signal.

In embodiments, the SRO circuit is at least one of a Collpitsoscillator, a Hartley oscillator, a Pierce oscillator, and a Clapposcillator.

According to a second aspect, and in accordance with advantages andeffects described herein above with reference to the first aspect, thereis provided a unit that includes a receiver in accordance with the firstaspect. The processing device is configured to generate an activationsignal to transition the unit from a dormant state to an operativestate.

In embodiments, the unit comprises at least one of a wirelesscommunication device and an imaging device. The processing device maythen be configured to generate the activation signal to transition theat least one of the wireless communication device and the imaging devicefrom a dormant state to an operative state.

In a further embodiment, the wireless communication device includes acommunication receiver that is electrically coupled to the sensor of thereceiver. This communication receiver may be configured to receive andprocess further detector signals from the sensor when the communicationdevice has transitioned into the operative state. The same sensor maythus be shared by the circuit and the communication receiver, whichlowers the spatial footprint and number of components.

In further embodiments, the unit is configured to be deployed underwateron or in a submerged earth layer or a submerged structure. In this case,the imaging device may be an underwater photogrammetric camera that isconfigured to acquire image data of the surroundings of the unit.Alternatively or in addition, the communication receiver may be anoptical receiver that is configured to receive wireless opticalcommunication signals that approach the unit through the surroundingfluid medium.

In an alternative embodiment, the unit is configured to be deployedunderwater on or in a submerged earth layer or a submerged structure,and the unit comprises an mechanical release that is configured tocreate a temporal connection for holding the unit at or near the earthlayer or structure. In this case, the sensor may be an acoustic sensorcoupled to the mechanical release. The receiver may then be configuredto provide the activation signal to the mechanical release, in order toremove the temporal connection and allow the unit to ascent from theearth layer or structure.

According to a third aspect, and in accordance with advantages andeffects described herein above with reference to the first aspect, thereis provided a method for transitioning a unit from a dormant state to anoperative state. The unit comprises a SRO circuit, a processing device,and a sensor that is one of an optical sensor, an acoustic sensor, and amagnetic field sensor. The method comprises:

-   -   receiving, with the sensor, a wireless signal from an external        source in the vicinity of the unit;    -   generating, with the sensor, a detector signal in response to        the received wireless signal;    -   receiving, with the SRO circuit, the detector signal;    -   causing the SRO circuit to electrically oscillate with a        constant SRO frequency and with a SRO amplitude that changes        when a carrier frequency of the detector signal substantially        matches the SRO frequency;    -   monitoring, with the processing device, the SRO amplitude in        time;    -   generating, with the processing device, an activation signal        when a temporal characteristic of the monitored SRO amplitude        matches with a predetermined reference pattern, and    -   using the activation signal to transition the unit from the        dormant state to the operative state.

In an embodiment, the method comprises:

-   -   causing the SRO circuit to electrically oscillate with a varying        SRO amplitude during successive time intervals, including        quenching the SRO amplitude at a start of each time interval,        followed by causing the SRO amplitude to rise during said time        interval, wherein a rising rate for the SRO amplitude within        said time interval is magnified when the carrier frequency of        the detector signal substantially matches the SRO frequency, and    -   determining, with the processing device, characteristic times        for the rise of the SRO amplitude during each of the time        intervals, to derive the temporal characteristic.

In a further embodiment, the method comprises:

-   -   comparing the SRO amplitude with a reference amplitude, and        generating a comparator signal with a distinct value if the SRO        amplitude exceeds the reference amplitude.

In yet a further embodiment, the method comprises:

-   -   receiving and storing a said comparator signal with a sequence        of consecutive distinct values in time;    -   comparing the sequence of consecutive distinct values to said        predetermined reference pattern, and    -   generating the activation signal when the sequence of        consecutive distinct values matches said predetermined reference        pattern.

In embodiments, the microcontroller is electrically coupled to the SROcircuit, and the method further comprises:

-   -   generating, with the microcontroller, a driving signal, and    -   imposing the driving signal together with the detector signal        onto the SRO circuit.

In further embodiments, the driving signal is a periodically rising andfalling signal, and the method further comprises:

-   -   periodically quenching and inducing oscillations in the SRO        circuit during each of successive time intervals.

Further aspects relate to a computer program product and a computerreadable medium, which provide and store instructions for carrying outthe method according to the third aspect.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments will now be described, by way of example only, withreference to the accompanying schematic drawings in which correspondingreference symbols indicate corresponding parts. In the drawings, likenumerals designate like elements.

FIG. 1 schematically shows a unit with a receiver according to anembodiment;

FIGS. 2 and 3 present schematic views of receivers according toembodiments;

FIG. 4 schematically illustrates signal waveforms for various componentsin an operational underwater unit;

FIG. 5 shows an example of a SRO circuit, and

FIG. 6 schematically shows a unit with a receiver according to anotherembodiment.

The figures are meant for illustrative purposes only, and do not serveas restriction of the scope or the protection as laid down by theclaims.

DESCRIPTION OF EMBODIMENTS

The following is a description of certain embodiments of the invention,given by way of example only and with reference to the figures.

FIG. 1 schematically shows an embodiment of a monitoring unit 20deployed underwater. The unit 20 is immersed in a body of seawater 10,and is positioned on a surface 14 that forms a water-soil interfacebetween the seawater 10 and the seabed 12 below. Such a unit 20 may alsobe placed on man-made submerged structures in/on the seabed 12, forinstance on wellheads and production manifolds that form part of asubsea oil extraction system, and may cooperate with similar units (notshown) that are deployed in the vicinity.

The unit 20 includes a photogrammetric camera 26 enclosed within a rigidtransparent dome on a top side of the unit. A medial part of the housingof the unit 20 is also made of rigid and optically transparent material,and accommodates an optical communication receiver 22 and an opticalcommunication transmitter 24. In this example, the optical receiver 22and transmitter 24 are configured to communicate via wireless lightsignals having wavelengths substantially in an optical range of 300nanometers to 600 nanometers because optical signals with suchwavelengths are best transmitted through seawater. They areamplitude-modulated at a frequency of, for instance, 800 kHz torepresent the central carrier frequency, and further modulated aroundthis carrier frequency to convey data, e.g. by on/off key modulation.Other modulation frequencies than 800 kHz can be chosen if desired.

In an initial deployment stage for the system, the unit 20 is placed onthe seabed 12, for instance by an underwater vehicle. To conserveelectrical power, the deployed unit 20 remains in a dormant state forextended times, but may be woken up by an underwater vehicle 16 enteringthe deployment site. FIG. 1 illustrates an exemplary ROV 16, but thismay also be a different type of vehicle e.g. an autonomous underwatervehicle (UAV). The ROV 16 may include a wireless optical communicationdevice with an optical transmitter 18, which is configured tocommunicate with the unit 20. The ROV 16 may move within communicationrange of the unit 20 and emit an appropriate optical signal 28 towardsthe unit 20, to cause the unit 20 to transition from the dormant stateinto an operative state. Once activated, the unit 20 may be requestedvia optical transmission by the ROV 16 to execute various monitoringand/or data acquisition functions. The unit 20 may for instance beordered to acquire images using its camera 26, and may be ordered totransmit acquired data to the ROV 16 or to other observation unitswithin range using its signal transmitter 24.

FIG. 2 shows an embodiment of a receiver 30, which is integrated withthe optical receiver 22, and is connected to a sensor 32 that is usedfor reception of optical communication signals 28. In this example, thesensor 32 is a SiPM sensor, which includes an array of reverse biasedavalanche photodiode (APD) elements that are connected in parallelbetween a common cathode and a common anode of a sensor frontend circuit23. Sensor 32 produces an output signal 40 in response to the receivedoptical signals 28. The receiver 30 is configured to generate anactivation signal 54 in response to a predetermined pattern in theoutput signal 40 generated by the sensor 32. This activation signal 54causes the unit 20, shown in FIG. 1, to transition from a dormant statein which the communication receiver 22, the communication transmitter24, and the camera 26 are deactivated, to an operative state in whichthese components 22-26 are energized and functional.

Receiver 30 has low power requirements, and comprises, in this example,a super regenerative oscillator (SRO) circuit 34, a comparator 36, and amicrocontroller 38. In this example, the SRO circuit 34 may be formed bya circuit comprising a single transistor with a power consumption in themilliwatt range.

In general, SRO 34 is a super regenerative oscillator comprising afrequency selective element and a gain element. The frequency selectiveelement may be implemented using any circuit that is commonly used inconstructing oscillators like LC tank circuits, RC delay circuits,quartz crystals, delay-lines, ceramic resonator, SAW filters, etc. Thefrequency selective element is tuned to the carrier frequency, e.g. 800kHz, of the optical communication signals. The gain element may beimplement using any amplifier like BJT transistors, FET transistors,operational amplifiers, tunnel diodes, etc. The gain of the gain elementis controlled by a driving signal 50.

The preferred embodiment is a single transistor oscillator, as shown inFIG. 5. Common oscillator designs, such as Colpitts, Hartley, Pierce,Clapp or any other oscillator types, can be used in the embodiments ofthe invention. However, other low power devices, such as low powermicrocontrollers or integrated circuits can also be used as oscillator.

The SiPM sensor 32 is configured to receive wireless optical signals 28from an external light source in the vicinity of the unit 20, e.g. fromROV transmitter 18 or a transmitter of a nearby unit.

The SRO circuit 34 is electrically coupled to the sensor 32, to receiveor sample the detector output signal 40. The SRO 34 is configured toelectrically oscillate at a substantially constant SRO resonancefrequency but with a changing SRO amplitude As. The oscillation forms anoutput signal 42 of the SRO 34. When the sensor 32 receives an opticalsignal 28 with a carrier frequency that substantially matches the SROoscillation frequency, e.g. 800 kHz, the oscillating detector signal 40will cause the oscillatory behavior of the SRO 34 to change.

The comparator 36 is electrically coupled to the SRO 34 and to a source44 that supplies a signal, e.g. voltage, with a reference amplitudeAref, which is used as a threshold value. The comparator 36 functions asan envelope detector, which receives the SRO output 42, measures theoscillation amplitude As in the SRO output 42, and compares theoscillation amplitude As with the reference signal amplitude Aref. Thecomparator 36 generates a distinct comparator output signal 46 inresponse to detecting that the oscillation amplitude As has reached thethreshold value Aref.

The microcontroller 38 is electrically coupled to the comparator 36, toallow comparator signal 46 to be fed to the microcontroller 38. Duringoperation, the microcontroller 38 detects and tracks transitions in thecomparator signal 46, and determines delay times Ti between consecutivetransitions. The microcontroller 38 monitors a sequence of transitionsin the comparator signal 46 in consecutive time intervals Δti,determines a sequence of delay times Ti associated with each intervalΔti, and repetitively compares the most recent sequence of transitionsin the comparator signal 46 (or delay times Ti) to a reference sequencesignal 52 of which the variation in time resembles a predetermined code.

When the microcontroller 38 establishes that a sequence of times Ti inthe comparator signal 46 matches the reference sequence signal 52according to a predetermined metric, the microcontroller 38 generatesand dispatches an activation signal 54 to the unit 20, e.g., to one ormore of optical receiver 22 (23), optical transmitter 24, and camera 26,thereby causing the unit 20 to transition from its dormant state intoits operative state. So, the reference sequence signal 52 functions as awake-up code check signal.

In the example of FIG. 2, the microcontroller 38 is also electricallycoupled to the SRO 34 and configured to generate and impose onto the SRO34 the driving signal 50 that is superimposed upon the detector signal40. This driving signal 50 is periodic and subdivided into time slotsΔti of identical lengths, by means of a clock signal 48 furnished to themicrocontroller 38. This driving signal 50 helps to quench and induceelectrical oscillation of the SRO 34 in each time slot Δti in aperiodically paced manner.

Alternatively, the driving signal 50, which functions as a quench rampsignal, can be generated by and supplied to the SRO 34 by a separatededicated circuit, not shown, outside of microcontroller 38. Such adedicated circuit can be a simple digital or analogue circuit.

As a further alternative, a “self-quenched” architecture can beemployed, in which the SRO 134 itself generates its own quench signal.This is shown in FIG. 3 where the output signal 142 is fed back to SROcircuit 134 as drive signal 150 and used as a self-quenching signal. Forthe rest, FIG. 3 shows the same circuit as FIG. 2, with like featuresdesignated by similar reference numerals preceded by 100 to distinguishthe embodiments.

When the system is in use, optical transmitter 18 (FIG. 1), if itdesires to transmit a logic “1” level, transmits a light signal which israpidly switched on and off at the above mentioned carrier frequency ofe.g. 800 kHz. When the optical transmitter 18 desires to transmit a “0”,it is configured such that its light source remains off.

The carrier frequency can be in the range of 10 Hz to 1 GHz. A singlebit in the code word contains multiple on/off sequences of the carrier.The bit rate, measured in bits per second is thus lower than the carrierfrequency and in the range of almost 0 bps to 100 Mbps

The preferred embodiment uses a carrier frequency of 800 kHz and a bitrate of 10 bps.

FIG. 4 illustrates typical signal waveforms as a function of time, whichare associated with the operation of the receiver, for instance theexemplary receiver 30 illustrated in FIG. 2. The first waveform Srrepresents a time sample of the detector current 40 over threeconsecutive time slots Δti (i=1, 2, 3). Waveform Sr as shown in FIG. 4comprises a first time slot Δt1 in which no signal is present, a secondtime slot Δt2 in which a signal is present oscillating with the abovementioned carrier frequency, and time slot Δt3 in which no signal ispresent. Thus, a code word “010” has been received by sensor 32. As canbe seen, each time slot Δti is used for transmitting one bit and the bitrate is lower than the carrier frequency.

The second waveform Sd in FIG. 4 represents a synchronous time sample ofan example of the driving signal 50 generated by the microcontroller 38.The driving signal 50 controls the gain of SRO 34. In this example, thesecond waveform Sd is formed as a periodic sawtooth signal, wherein theperiods coincide with the time slots Δti and in which each period isformed by a steeply falling edge that quenches SRO oscillations and aslowly rising edge that induces SRO oscillations.

The third waveform Ss represents a synchronous sample of oscillatingoutput signal 42 of the SRO 34, for which the SRO oscillation amplitudeenvelope As is also indicated. The driving signal 50 frommicrocontroller 38 alternatingly induces and quenches oscillations inthe SRO 34. As the driving signal 50 slowly ramps up, the oscillatingoutput signal 42 also starts to build up.

The fourth waveform Sc represents a synchronous sample of the comparatoroutput signal 46. This output signal 46 is formed by the comparator 36,via comparison of the oscillation amplitude As of output signal 42 withreference signal amplitude Aref. A time delay required for theoscillation signal amplitude As to rise from (virtually) zero to thereference signal amplitude Aref will vary, depending on the amplitude Arof the detector current 40, and may be described by a characteristictime Ti for each time slot Δti. If the sensor 32 is not receiving anyoptical signal (as in slots Δt1 and Δt3) and thus does not generate asubstantial current 40, it takes the SRO 34 a characteristic time T1 orT3 (T1=T3) to bring the SRO oscillation signal amplitude As to thereference level Aref. If the sensor 32 does detect an optical signal 28,it takes the SRO 34 a second characteristic time T2 shorter than each ofthe times T1, T3 to bring the oscillation amplitude As to the referencelevel Aref. In other words, the time it takes for the oscillations toexceed reference level Aref is influenced by the carrier amplitude ofdetector signal 40. The greater the carrier amplitude of detector signal40, the faster the amplitude of the oscillations of the SRO output willreach reference level Aref.

As the driving signal 50 falls to its lowest levels, the oscillations inSRO 34 are stopped or “quenched”. Because of the periodicity of controlsignal 50 the oscillations in SRO 34 are thus periodically started andquenched.

The frequency of driving signal 50 should be less than the carrierfrequency. A person skilled in the art would recognize that the time ittakes for the oscillations in the SRO output signal 42 to build up isalso dependent on the quality factor Q of the frequency selected elementinside the SRO 34. The higher the Q the slower the buildup ofoscillations in the SRO output signal 42. The frequency of the drivingsignal 50 must thus be tuned to the Q of the frequency selective elementin SRO 34. At the same time, the frequency of the driving signal 50 mustbe at least equal or preferably higher than the bit rate in order tosatisfy the Nyquist criteria for alias-free sampling.

In an example, the driving signal has a frequency in a range of 750-2500Hz, preferably in a range of 1000-2000 Hz, e.g. 1500 Hz.

A person skilled in the art would thus understand that the frequencyselectivity of the SRO circuit, the maximum bit rate and the carrierfrequency are all related. The optimum SRO circuit is thus a compromisebetween all these parameters.

The SRO circuit thus converts carrier amplitude variations in thedetector signal 40 into pulse-width variations in comparator signals 46.

Processing device 38 receives a clock signal from clock 48 and measuresthe pulse-width variations in the comparator output signal 46 bycounting the number of clock pulses in the clock signal between therising and falling edges of the comparator signal 46, cf. signal Sc inFIG. 4.

The pulse-width variations of the comparator signals 46 form in time thereceived code word. This code word is compared by processing device 38against the reference code word 52. When the received code word and thereference code match, the processing device 38 generates activationsignal 54 and device 20 is woken up.

So, the characteristic time Ti depends on the amplitude Ar and frequencyof the detector current 40. In this manner, an increased intensity ofreceived light signal is transformed into a shortened characteristictime Ti.

FIG. 5 shows an example of a SRO circuit 134. The SRO circuit 134 shownin FIG. 5 is a Colpitts oscillator. The SRO circuit 134 comprises acapacitor C1 connected between an input terminal and ground and aninductor L2 connected with a first terminal to the input terminal andwith a second terminal to a first terminal of a capacitor C2 of whichits second terminal is connected to ground. A capacitor C3 has a firstterminal connected to the first terminal of capacitor C2 and its secondterminal connected to a first terminal of a resistor R2. A secondterminal of resistor R2 is connected to ground. First terminal ofresistor R2 is connected to a base of a transistor Q1. A resistor R1 hasa first terminal connected to a power supply V1 and a second terminalconnected to the base of transistor Q1. An inductor L1 has a firstterminal connector to the power supply V1 and a second terminalconnected to a collector of the transistor Q1. The collector oftransistor Q1 is fed back to the input of the SRO circuit. Transistor Q1has an emitter connected to a first terminal of a resistor R3 and afirst terminal of a capacitor C5. A second terminal of resistor R3 and asecond terminal of capacitor C5 are both connected to ground.

The input terminal of SRO 134 is configured to receive output signal 140of sensor 132. The collector of transistor Q1 is configured to provideoutput signal 142. Transistor Q1 is also an amplifier wherein the baseis the input of the amplifier and the collector is the output of theamplifier.

Transistor Q1 is thus operated in the common emitter configuration. L2,C1 and C2 form a frequency selective circuit that feeds the outputsignal of the amplifier into the input of the amplifier thereby forminga complete oscillator. The output signal 142 causes varying currentsthrough the transistor Q1 which are integrated by C5. When oscillationsincrease, the current through Q1 increases and the voltage over C5increases. At some point the voltage over C5 becomes so large thatvoltage difference between the base and emitter of Q1 becomes so smallthat transistor Q1 stops conducting and the oscillations are thusquenched. When the oscillations 142 have stopped, C5 is dischargedthrough R3 causing the transistor Q1 to slowly turn on again hencecreating a slow ramp up of the gain of Q1. This Colpitts oscillator isof the self-quenching type and can, thus, be used in the setup of FIG.3.

FIG. 6 schematically shows a unit 220 with a receiver 230 according toanother embodiment. Features in the unit 220 that have already beendescribed above with reference to the previous unit embodiments (and inparticular FIGS. 1-5) may also be present in the unit 220 in FIG. 6, andwill not all be discussed here again. Like features are designated withsimilar reference numerals preceded by 200 to distinguish theembodiments.

This exemplary unit 220 includes various monitoring sensors (not shown)that are enclosed within a rigid cylindrical housing, which is suspendedupright in the seawater 210 near the seafloor 212 by means of a floatingbody 221 connected to an upper end of the housing. On a lower side ofthe housing, the unit 220 is held close to the seafloor 212 by means ofa cable 223 and a weight 225. The unit 220 comprises a mechanicalrelease 231 that temporarily maintains a connection with the cable 223.In this case, the sensor 232 is an acoustic sensor that is coupled tothe mechanical release 231. The receiver 230 is configured to detect anincoming acoustic signal 228 with an appropriate carrier wave frequencyand temporal characteristic from an external source 218 (e.g. andacoustic transmitter 218 from a nearby ROV 216), in a similar manner asdescribed above with reference to FIGS. 2-4. The receiver 230 respondsto such a signal 228 by providing an activation signal 254 to themechanical release 231, which energizes the release mechanism andremoves the temporal connection, thus allowing the unit 220 to ascentfrom the seafloor to the surface of 210 while leaving the cable 223 andweight 225 behind on the seafloor 212.

The receivers 30 as described above have the following advantages:

-   -   The receiver consumes only very little power. This especially        so, when the SRO is implemented with a single transistor.    -   In case of implementation with a single transistor, the receiver        is very simple and is thus more reliable and easier to design        and implement.    -   The receiver is frequency selective, i.e, it only responds to a        received signal of a predetermined frequency.    -   The receiver has a high gain, so amplifies weak signals.    -   The receiver has a high dynamic range and is, thus, able to        receive strong signals (or receive weak signals in the presence        of unwanted strong signals).

The present invention may be embodied in other specific forms withoutdeparting from its essential characteristics. The described embodimentsare to be considered in all respects only as illustrative and notrestrictive. The scope of the invention is, therefore, indicated by theappended claims rather than by the foregoing description. It will beapparent to the person skilled in the art that alternative andequivalent embodiments of the invention can be conceived and reduced topractice. All changes which come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

For instance, the examples described herein above, the receiver withsensor and super regenerative oscillator formed part ofpower-constrained units. Those of skill in the art will understand thatthe proposed receiver with sensor and super regenerative oscillator maybe included in systems that are not power-constrained, but which are forinstance supplied with mains electric power.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), aProgrammable System on Chip (PSoC), a field programmable gate array(FPGA) or other programmable logic device, discrete gate or transistorlogic, discrete hardware components, or any combination thereof designedto perform the functions described herein. A general purpose processormay be a microprocessor, any conventional processor, controller,microcontroller, or state machine. A processor may also be implementedas a combination of computing devices. The steps of a method oralgorithm described in connection with the embodiments disclosed hereinmay be embodied directly in hardware, in a software module executed by aprocessor, or in a combination of the two.

LIST OF REFERENCE SYMBOLS

Similar reference numbers that have been used in the description toindicate similar elements (but differing only in the hundreds) have beenomitted from the list below and in the claims, but should be consideredimplicitly included.

10 body of water (e.g. seawater)

12 submerged earth layer (e.g. seabed)

14 submerged earth surface

16 underwater vehicle (e.g. ROV or UAV)

18 vehicle transmitter

20 unit (e.g. underwater observation or communication unit)

22 communication receiver

23 receiver frontend

24 communication transmitter

26 imaging device (e.g. underwater photogrammetric camera)

28 wireless signal (e.g. from underwater vehicle)

30 receiver or wake-up receiver

32 sensor (e.g. light/acoustic/magnetic sensor)

34 SRO circuit

36 envelope detector (e.g. comparator)

38 microcontroller

40 detector signal

41 further detector signal

42 SRO output signal

44 reference amplitude source

46 comparator output signal

48 clock signal

50 driving signal

52 reference pattern

54 activation signal

221 float

223 cable

225 weight

231 mechanical release

Ar detector signal amplitude

Aref reference amplitude

Ac comparator signal amplitude

As SRO oscillation amplitude

Sr detector signal waveform

Sd driving signal waveform

Ss SRO signal waveform

Sc comparator output waveform

Δti SRO oscillation interval (i∈N)

Ti characteristic time in interval Δti

1. A receiver configured to provide an activation signal to a device inorder to transition the device from a dormant state to an operativestate, wherein the receiver comprises: a sensor, being one of an opticalsensor, an acoustic sensor, and a magnetic field sensor, wherein thesensor is configured to receive a wireless signal from an externalsource and to generate a detector signal in response to the receivedwireless signal; a super regenerative oscillator (SRO), circuit,electrically coupled to the sensor to receive the detector signal, andconfigured to electrically oscillate with a constant SRO frequency andwith a SRO amplitude that changes when a carrier frequency of thedetector signal substantially matches the SRO frequency, and aprocessing device, configured to monitor the SRO amplitude in time, andto generate the activation signal when a temporal characteristic of themonitored SRO amplitude matches a predetermined reference pattern. 2.The receiver according to claim 1, wherein the SRO circuit is configuredto electrically oscillate with a varying SRO amplitude during successivetime intervals, wherein the SRO amplitude quenches at a start of eachtime interval, and subsequently rises during said time interval, whereina rising rate for the SRO amplitude within said time interval ismagnified when the carrier frequency of the detector signalsubstantially matches the SRO frequency, and wherein the processingdevice is configured to determine characteristic times for the rise ofthe SRO amplitude during each of the time intervals to derive thetemporal characteristic.
 3. The receiver according to claim 2, whereinthe processing device comprises a comparator that is configured toreceive an output signal with said varying SRO amplitude from the SROcircuit, and is configured to output a comparator signal with a distinctvalue if the varying SRO amplitude exceeds a reference amplitude.
 4. Thereceiver according to claim 3, further comprising a microcontroller thatis electrically coupled to the comparator and configured to: receive andstore said comparator signal with a sequence of consecutive distinctvalues in time; compare the sequence of consecutive distinct values tosaid predetermined reference pattern, and generate the activation signalwhen the sequence of consecutive distinct values matches saidpredetermined reference pattern.
 5. The receiver according to claim 4,wherein the microcontroller is electrically coupled to the SRO circuit,and configured to generate and impose onto the SRO circuit a drivingsignal that is superimposed upon the detector signal.
 6. The receiveraccording to claim 5, wherein the driving signal forms an alternatinglyrising and falling signal that is configured to periodically induce andquench oscillations in the SRO circuit, wherein the driving signal mayfor instance be a quench-ramp signal with a sawtooth profile.
 7. Thereceiver according to claim 6, wherein the sensor is an optical sensorincluding a plurality of avalanche photodiode, APD, elements, whereinthe APD elements may for instance be arranged into an array to form asilicon photomultiplier, SiPM, sensor.
 8. The receiver according toclaim 1, wherein the SRO circuit comprises a frequency selective elementand a gain element, which frequency selective element is tuned to saidcarrier frequency.
 9. The receiver according to claim 8, wherein a gainof the gain element is controlled by said driving signal
 10. Thereceiver according to claim 1, wherein said SRO circuit is at least oneof a Collpits, Hartley, Pierce, and Clapp oscillator.
 11. The receiveraccording to claim 1, wherein the receiver is a wake-up receiver.
 12. Aunit comprising a receiver according to claim 1, wherein the processingdevice is configured to generate an activation signal to transition theunit from a dormant state to an operative state.
 13. The unit accordingto claim 12, comprising at least one of a wireless communication deviceand an imaging device wherein the processing device is configured togenerate the activation signal to transition the at least one of thewireless communication device and the imaging device from a dormantstate to an operative state.
 14. The unit according to claim 13, whereinthe wireless communication device includes a communication receiver thatis electrically coupled to the sensor of the receiver, and is configuredto receive and process further detector signals from the sensor when thecommunication device has transitioned into the operative state.
 15. Theunit according to claim 13, wherein the unit is configured to bedeployed underwater on or in a submerged earth layer or a submergedstructure, wherein the imaging device is an underwater photogrammetriccamera for acquiring image data of the surroundings of the unit, and/orwherein the communication receiver is an optical receiver configured toreceive wireless optical communication signals that approach the unitthrough the surrounding fluid medium.
 16. The unit according to claim12, wherein the unit is configured to be deployed underwater on or in asubmerged earth layer or a submerged structure, wherein the unitcomprises an mechanical release that is configured to create a temporalconnection for holding the unit at or near the earth layer or structure,wherein the sensor is coupled to the receiver and the receiver isconfigured to provide the activation signal to the mechanical release toremove the temporal connection and allow the unit to ascent from theearth layer or structure.
 17. A method for transitioning a unit from adormant state to an operative state, wherein the unit comprises a sensorthat is one of an optical sensor, an acoustic sensor, and a magneticfield sensor, a super regenerative oscillator (SRO), circuit, and aprocessing device, wherein the method comprises: receiving, with thesensor, a wireless signal from an external source in the vicinity of theunit; generating, with the sensor, a detector signal in response to thereceived wireless signal; receiving, with the SRO circuit, the detectorsignal; causing the SRO circuit to electrically oscillate with aconstant SRO frequency and with a SRO amplitude that changes when acarrier frequency of the detector signal substantially matches the SROfrequency; monitoring, with the processing device, the SRO amplitude intime; generating, with the processing device, an activation signal whena temporal characteristic of the monitored SRO amplitude matches apredetermined reference pattern, and using the activation signal totransition the unit from the dormant state to the operative state. 18.The method according to claim 17, comprising: causing the SRO circuit toelectrically oscillate with a varying SRO amplitude during successivetime intervals, including quenching the SRO amplitude at a start of eachtime interval, followed by causing the SRO amplitude to rise during saidtime interval, wherein a rising rate for the SRO amplitude within saidtime interval is magnified when the carrier frequency of the detectorsignal substantially matches the SRO frequency; determining, with theprocessing device, characteristic times for the rise of the SROamplitude during each of the time intervals, to derive the temporalcharacteristic.
 19. The method according to claim 18, further comprisingcomparing the SRO amplitude with a reference amplitude, and generating acomparator signal with a distinct value if the SRO amplitude exceeds thereference amplitude.
 20. The method according to claim 19, furthercomprising: receiving and storing said comparator signal with a sequenceof consecutive distinct values in time; comparing the sequence ofconsecutive distinct values to said predetermined reference pattern, andgenerating the activation signal when sequence of consecutive distinctvalues matches said predetermined reference pattern.
 21. The methodaccording to claim 17, wherein the microcontroller is electricallycoupled to the SRO circuit, and wherein the method comprises:generating, with the microcontroller, a driving signal, and imposing thedriving signal together with the detector signal onto the SRO circuit.22. The method according to claim 21, wherein the driving signal is aperiodically rising and falling signal, and wherein the methodcomprises: periodically quenching and inducing oscillations in the SROcircuit during each of successive time intervals.
 23. A non-transitorycomputer readable medium, storing instructions that, when executed by aprocessor, will cause the processor to: receiving, with a sensor, awireless signal from an external source in a vicinity of a unitgenerating, with the sensor, a detector signal in response to thereceived wireless signal; receiving, with a super regenerativeoscillator (SRO) circuit, the detector signal; causing the SRO circuitto electrically oscillate with a constant SRO frequency and with a SROamplitude that changes when a carrier frequency of the detector signalsubstantially matches the SRO frequency; monitoring, with the processor,the SRO amplitude in time; generating, with the processor, an activationsignal when a temporal characteristic of the monitored SRO amplitudematches a predetermined reference pattern, and using the activationsignal to transition the unit from a dormant state to an operativestate.